Technical Abstract:
Reduced tillage is being examined as a means of enhancing soil carbon and mitigating greenhouse gas (GHG) emissions. There is relatively little information regarding tillage effects on emissions of nitrous oxide (N2O) and methane (CH4), which have higher global warming potentials than carbon dioxide (CO2). We used chambers to measure N2O and CH4 fluxes in plots maintained under differing tillage treatments since 1991. Emissions of N2O following broadcast urea (BU) application were higher under no till (NT) and conservation tillage (CsT) compared to conventional tillage (CT). In contrast, following anhydrous ammonia (AA) injection,N2O emissions were higher under CT and CsT compared to NT. Emissions following urea ammonium nitrate (UAN) application did not vary with tillage. Total growing season non-CO2 GHG emissions were dominated by N2O, and were equivalent to soil C losses of 0.07 – 0.50 Mg C ha-1 y-1. Uptake of CH4 during the drier of the two seasons (2003) was two to three times higher than during 2004. Emissions of N2O from AA-amended soils exceeded emissions from the UAN and BU treatments. This study demonstrates that tillage effects on N2O emissions depend on fertilizer management and that non-CO2 GHG emissions can contribute substantially to the total GHG budget of agro-ecosystems in the upper mid west U.S.